Spotting a day or two into your PCOS treatment is common. Metformin-based medicines like yours can cause this kind of light bleeding while your body adjusts. Your cough and cold are separate issues. Coughing itself does not create pressure that causes vaginal spotting, so that part isn't the cause.
Next Steps
Keep taking your tablets as prescribed. Note how many days the spotting lasts and whether it gets heavier. If it continues past a week or turns into heavier bleeding, tell your gynaecologist so they can review your treatment.
Health Tips
See a doctor sooner if the spotting becomes as heavy as a period, or if fever develops alongside it.